package com.imooc.distributedemo.rithm;

/**
 * implementation for heap sort
 */
public class HeapSort {

    public static void sort(int[] arr){
        int n = arr.length;
        // build heap (rearrang array)
        for (int i = n/2-1; i >= 0; i--) {
            heapify(arr,n,i);
        }
        // one by one extract element from heap
        for (int i = n-1; i >0 ; i--) {
            int temp = arr[0];
            arr[0] = arr[i];
            arr[i] = temp;
            // call max heapify on the reduced heap
            heapify(arr,i,0);
        }
    }

    // To heapify a subtree rooted with node i which is
    // an index in arr[]. n is size of heap
    private static void heapify(int[] arr, int n, int i) {
        int largest = i;
        int l = 2*i+1;
        int r = 2*i+2;
        // if left child larger than root
        if(l<n&&arr[l]>arr[largest]){
            largest = l;
        }

        // If right child is larger than largest so far
        if(r<n&&arr[r]>arr[largest]){
            largest = r;
        }

        // if largest is not root
        if(largest!=i){
            int swap = arr[i];
            arr[i] = arr[largest];
            arr[largest] = swap;
            // Recursively heapify the affected sub-tree
            heapify(arr, n, largest);
        }
    }

    /* A utility function to print array of size n */
    public static void printArray(int arr[]){
        int n = arr.length;
        for (int i = 0; i < n; ++i) {
            System.out.print(arr[i]+" ");
        }
        System.out.println();
    }

    public static void main(String[] args) {
        int arr[] = { 12, 11, 13, 5, 6, 7 };
        int n = arr.length;
        HeapSort ob = new HeapSort();
        ob.sort(arr);
        System.out.println("sorted array is:");
        printArray(arr);
    }
}
